Dark Magic's Derivative Spells

"So... you're this—uh—so-called 'Magic Resonance Library' administrator?" Yulian stepped closer.

After a long pause, the black cat finally spoke, its voice low and lazy, tinged with a French accent (likely to match Yulian's own): "You can call me Murphy—not the 'Murphy's Law' Murphy, but Muff—though you do tend to have rotten luck. I'm the curator, librarian, cataloger, borrowing inspector, and... the faithful recorder of your inner shame."

"What? What was that last one?"

"When you have questions weighing on your mind, I can record them and find you the answers." The black cat's voice was flat.

"Any question?" Yulian asked hesitantly.

"Remember! This is the Magic Resonance Library, meant to improve your magical skill. I have zero interest in your personal life unrelated to magic—like that thing with Leah in your memories, or the time you peeked at the neighbor girl bathing as a kid, or..."

"Stop, stop!" Yulian cut in urgently. "If you have no interest, how do you know so much?"

Seeing the black cat finally shut up, Yulian breathed a sigh of relief and looked around. "So what's this place actually for?"

Murphy hopped off the bookshelf, landing lightly, and paced as he spoke: "Simply put, every time you truly understand a magical concept—whether through brains, luck, or getting chewed out by a teacher—a book generates here automatically."

Murphy moved with the elegance of a model. "These books are detailed answers to the questions you care about. They're echoes of your magic and footprints of your growth."

"Great, so if I read the books, I'll instantly know the spells I can't do?" Yulian perked up. "How about starting with a... Patronus Charm book." No transmigrator worth their salt skipped that.

"Or maybe a 'Legilimency' book—since all transmigrators practice that first, afraid of running into some unreasonable prop like the Sorting Hat or a creepy old geezer like Dumbledore poking around in your head."

Murphy shot him a glance, amber eyes flashing disdain, as if to say, "Pfft, what's there in you worth poking around for?"

"The library only stores what you can master. It speeds up your learning and improves results. For example, with a Levitation Charm, you could practice repeatedly without the library and still get it, but with the book's guidance, you'll grasp it faster, do it better, float bigger things, control more precisely, and so on."

"If you just memorize by rote or try to get something for nothing, the book will be blank. And..." Murphy lowered his voice, "the more important the secret, the harder the book is to open. Like the books behind that door..."

Yulian looked up and saw, at the far end of the library, a bronze door tightly shut.

"Is that Dark Magic in there?" Yulian rubbed his hands excitedly.

"What, you think Dark Magic is advanced magic?"

"Then what is it?" Though Murphy's contemptuous look irked him, Yulian, following the principle of when in Rome, bowed and scraped.

"Don't rush. You're not at that level yet." Murphy yawned, lying on the floor, and spoke lazily.

"So with no books now, I just wait around?"

Murphy rolled his eyes. "Fine. Young Wizards usually start with the Levitation Charm. Let me show you that book first."

As he spoke, a book materialized out of thin air on the shelf behind him. Its spine glowed faintly blue.

"Great!" Yulian quickly grabbed the book from the shelf—Why Feathers Always Want to Hit Your Face.

"You sure this is for practicing the Levitation Charm?"

"Sure, certain, and absolutely positive."

This book indeed helped Yulian a lot, not only pointing out the key points for practicing the Levitation Charm but also being especially targeted.

After that, Alphard, convinced his grandson was a magical prodigy, accelerated his teaching.

One night, pinewood crackled in the Chamber of Secrets' fireplace, stretching the shadows of the two men long and making the darkness beside the hearth especially thick—deep enough to swallow the candlelight.

Maybe it was just Yulian's imagination, but he felt something writhing in that darkness, like a sleeping beast slowly turning over.

Alphard didn't pull out any basic spellbooks as usual. Instead, he paced to the oak liquor cabinet and pressed lightly under the third drawer.

With a soft click, a hidden compartment popped open, revealing a leather-bound notebook. The cover bore no text, only an embossed Black Family Crest—a winged Gryphon with blazing eyes, as if ready to leap from the leather.

"What I'm teaching you today isn't covered in Hogwarts classes." The old man's voice was low and grave, like he was recounting a dusty family secret. "These are my notes from when I learned these spells as a youth. Use them as a reference."

Alphard opened the notebook. Yellowed pages held spell annotations in old-fashioned cursive English, with complex wand movement diagrams drawn beside them. Some spots even had red-ink warnings like "Prone to backfire here" or "Do not cast more than three times in a row."

"The first is the Shadow Deflection Charm, a Dark Magic derivative the Ministry of Magic classifies as an 'Unforgivable Curse'—Obscurum Flecto. I'll demonstrate. Take the notebook."

Yulian took the notebook, and the moment his fingertips touched the leather, his head buzzed—

Ding! Detected high-concentration Dark Magic knowledge source. Generating new book: <Shadow Deflection Charm for Beginners: How to Gracefully Bounce Curses Back at Enemies Without Getting Caught by the Ministry>.

In his mental space, the nearly empty Magic Resonance Library quietly lit up a lamp. On the shelf, a brand-new book slowly materialized, its cover black as night, its gold-stamped title gleaming.

Yulian's breath caught. He knew exactly what Dark Magic meant.

Like all transmigrators, Yulian didn't reject Dark Magic. In fact, he was secretly pleased and hoped for more—preferably starting maxed out on Unforgivable Curses, like in those fanfics.

Otherwise, how would he take on Voldemort later? That made perfect sense for a transmigrator, right?

Seeing Yulian's slightly odd expression, the old man explained, "Don't be afraid, child. Magic itself has no good or evil; it's the user's intent that matters."

"I'm not afraid," Yulian looked up, eyes bright. "I just thought pure-blood families started teaching with the three Unforgivable Curses."

Alphard's mouth twitched. "Huh? Didn't expect you to think that."

He rubbed his temples, as if recalling whether he'd been that cringey as a teen.

"Child, you need to know that even without making a Horcrux, using Unforgivable Curses will leave your soul broken and ugly—like a piece of cheese eaten by worms, whole on the outside but rotten within."

"Horcrux? What's a Horcrux? How do you make one?" Yulian blurted out, his eyes full of thirst for knowledge and a hint of foolish curiosity.